If you keep getting this error Conversion to Dalvik format failed: Unable to execute dex: java.nio.BufferOverflowException, then just add the Support Library. Right click on your project, then Android Tools -> Add Support Library… Then just follow the steps to install that.

I am using API 19 (Android 4.4), and I am not downgrading! =)

Ref: http://techlovejump.in/2013/11/how-to-solve-unable-to-execute-dex-java-nio-bufferoverflowexception-check-the-eclipse-log-for-stack-trace/